System for cooking fibrous material



T. L. DUNBAR 1,798,525

Filed Aug. 1, 1929 2 Sheets-Sheet l a y RESk M ox mam SYSTEM FOR COOKING FIBROUS MATERIAL March 31, 1931.

.xumhvmwq komwmgg .BNE BQBGQMN A n w m 8 wmwkomw z 3 R Iv a Y, llv A 35 3 w All kvsS .vkswwmk l H H H II I lI L w mm March 31, 1931. T. 1.. DUNBAR SYSTEM FOR COOKING FIBROUS MATERIAL Filed Aug. 2 Sheets-Sheet 2 Patented Mar. 31, 1931 UNITED STATES THOMAS LEONIDAS DUNBAR, OF WATERTOWN, NEW YORK SYSTEM FOR COOKING FIBROUS MATERIAL Application filed August 1, 1929. Serial No. 382,800.

This invention relates to improvements in the digestion of fibrous material, and more particularly to a novel system for recover ng acid and heat units, and for utilizing the same to precondition acid liquor that is to be fed to a digester or digesters.

Various schemes have been proposed for recovering acid and the heat umts thereof, and for pro-conditioning acid liquor, and the primary object of the present invention is to provide animproved system for thls purose. p Another object of the invention is to furnish a system of this character, in which cold acid liquor is continuously 'fed or sprayed into a chamber where it is contacted with relief gases and steam from a digester or d1- gesters, and the resulting mixture is continuously pumped from this chamber 1nto a high pressure accumulator in such manner that the pressure existing in the mixing chamber is always maintained at substantially atmospheric.

A further object is to provide a system of this type, in which all of the acid gas relieved from the digesters, as well as the heat units contained in said gases and in the steam which is discharged with the same, are recovered and utilized for preconditioning and Q pre-heating acid liquor which is thus rendered capable of initiating the cook in a digester or digesters.

With the foregoing objects outlined and with other objects in view which will appear as the description proceeds, my invention consists in the novel features hereinafter described in detail, illustrated in the accompanying drawings, and more particularly pointed out in the appended claims.

Referring to the drawings,

Fig. 1 is an elevation of the improved apparatus forming part of my system.

Fig. 2 is a similar View of a modification.

In the embodiment of the invention illustrated in Fig. 1, I have shown two digesters 3 and 4, but I wish it understood that any number of digesters may be employed with my improvements. The high pressure gas and steam relieved from the digesters during ..the cooking operation, passes out by way of valved branches 5, into a high pressure relief conduit 6, having a valve 7. Such high pressure material may flow under its'own pressure into acid liquor contained in an accumulator 8. This accumulator is maintained under super-atmospheric pressure, but usually,

at a pressure lower than that existing in the digesters during cooking, so that the high pressure relief gases and vapors may flow under their own pressure into the accumulator.

Low pressure relief gases and vapors are discharged from the digesters by way of valved branches 9, into a low pressure relief line 10, which terminates in a sprinkler head or rose 11, arranged in a mixing tank 12. In the latter, such gases and vapors are contacted with a shower of cold acid liquor which descends from a sprayer or rose 13, that is arranged within the mixing chamber at a higher elevation than the rose 11. The cold acid liquor may flow to thesprayer 13 by gravity from an elevated storage tank 14, but I prefer to feed the liquor from the storage tank by means of a pump 15 that is interposed in a valved conduit 16, one end of which is connected to the storage tank, and the other end of which joins the sprayer 13.

Where conditions permit, the high pressure relief gases and vapors may also be fed to the rose 11, by means of a valved pipe 17, and at such times, the valve 7 will be closed.

Of course, when high pressure gases and vapors are flowing to the mixing tank 12, the valves in the low pressure branches 9 will be closed, and on the other hand, when low pressure gases are flowing to the rose 11, the valves in the high pressure branches 5 will be closed.

Regardless of whether high pressure or low pressure gases and vapors are being discharged into the mixing chamber, as long as such discharge is taking place, the cold acid liquor will be forced continuously into the mixing chamber, so that it will absorb the gases, condense the vapors, and acquire the heat units contained in the gases and vapors,-

with the result that preheated and pre-conditioned acid liquor will be precipitated into the bottom portion of the mixing chamber 12. In order to maintain the interior of the chamber 12 at atmospheric or subatmospheric pressure, the liquor thus precipitated is continuously withdrawn from the chamber by means of a stand pipe 18, which leads from the lower portion of the chamber 12 to a down pipe 19 that is connected to the suction branch of a pump 20, which forces this preheated and pro-conditioned liquor through a'conduit 21, into the accumulator 8, against the pressure existing in the latter.

The pre-conditioned and preheated liquor which exists in the accumulator under superatmospheric pressure, is utilized for pre-cooking the fibrous material in the digesters, and for the purpose of illustration, let us assume that the digester 4 has just been filled with wood chips or the like. In such case, the prepared and heated liquor from the accumulator is forced by 'means of a pump 22, through a line 23, into one of the valved branches 24, which discharges the same into the bottom of the digesters. In this way, the chips in the digesters may be pre-cooked, or the cooking may be initiated before steam is turned into the digesters by the usual means (not shown).

To prevent the pressure in the accumulator 8 from reaching a dangerous or undesired degree, a pipe 25 leads from the top of the accumulator to the bottom of the storage tank 14, and this pipe is provided with an ordinary pressure operated valve 26. Consequently, when the valve 26 opens under the pressure existing in the accumulator, the fluid thus relieved, flows into the storage tank, and the gaseous portion of the same is absorbed by the cold acid liquor in this tank.

From the foregoing it will be apparent to those skilled in the art, that I have devised a novel system for relieving digesters, and for recovering the gases and heat units from the relief fluids, and that I utilize such gas and heat units in a special way, to preheat and pre-condition acid liquor which is to be stored in an accumulator under pressure, and is to be utilized in the pre-cooking of fibrous material. It will also be appreciated by those skilled in the art, that my system may take many forms, without departing from the spirit of the invention, as expressed in the annexed claims. As an example, the invention may be embodied in the form shown in Fig. 2. In this embodiment, a low pressure accumulator 30 is substituted forthe mixing tank 12, and all of the relief gases and vapors may flow from the digesters 31 (only one of which is shown), by way of a common valved relief line 32, into the lower end of the low pressure accumulator. The latter will always be partially filled with acid liquor. so that the gases in rising through the pool of liquor, will be practically all absorbed. Any gas which remains unabsorbed, in rising from the surface of the liquor pool, will be brought into counter-current contact with cold acid liquor which is sprayed into the upper end of the accumulator by means of a sprayer or rose 33, which is fed from the acid liquor storage tank 34 by means of a pipe 35 having an interposed pump 36. Like in the mixing tank 12, the cold acid liquor in the accumulator 30 will be pre-conditioned and preheated, and this liquor will be constantly withdrawn from the accumulator 30 by means of a pump 37 which is interposed in a pipe 38 that leads from the lower portion of the low pressure accumulator into the bottom of a high pressure accumulator 39. The operation of the pumps 36 and 37 are so controlled as to keep down the pressure in the accumulator 30, and to keep up the pressure in the accumulator 39. The pre-conditioned and preheated acid liquor tobe used in precooking chips or other fibrous material is forced from the accumulator 39 by means of a pump 40 into a conduit 41, which leads the same to the bottom of one or more of the digesters which have just been filled with chips or the like. I

In this modification also, a pipe 42 leads from the top of the accumulator 39 to the bottom of the acid liquor storage tank 34, and this pipe has a pressure operated valve 43, which functions in the same manner, and for the same purpose as the valve 26 in Fig. 1.

I have found it is much more beneficial, particularly with hot liquor, to pump the liquor into the bottom of the digester. As the liquor is pumped into the digester, it gradually rises until the/digester is filled, and this liquor passing through the raw material, such asAvood chips, is partially absorbed and, therefore, when side relief is begun at the start of the cook (through 45 in Fig. 1, or 44 in Fig. 2), liquor is released that is partially exhausted. This means that as the hot acid passes through the chips, greater efiiciency is-obtained than if the digester was filled with liquor from the top. for in the latter instance, when the side relief was started, fresh acid liquor would flow back to the mixing tank 12.

The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions, of excluding any equivalents of the features shown and described, or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What I claim and desire to secure by Letters Patent is:

1. In a system of the character described, discharging gases and vapors from a digester through a conduit into an enlarged mixing chamber, constantly feeding cold acid liquor into said chamber and thus utilizing the gases and vapors to pre-condition and prethrough a conduit into an enlarged mixing chamber, constantly feeding cold acid liquor into said chamber and thus utilizing the gases and vapors to pre-condition and pre-heat said liquor, withdrawing the pre-heated and preconditioned liquor from the chamber, and

thereby maintaining the latter at substantially atmospheric pressure, forcing the withdrawn liquor into an accumulator maintained at super-atmosphericpressure, and utilizing the pre-conditioned and pre-heated acid liquor from the accumulator to pre-cook fibrous material.

3. I11 a system of the character described,

passing cold acid liquor from a storage tank into a mixing chamber, discharging gases and vapors from a digester into the mixing chamber, and contacting the same in the latter with the acid liquor, whereby the acid liquor is pre-heated and pre-conditioned, withdrawing the preheated and pre-conditioned acid liquor from the mixing chamber and thereby preventing the pressure in the latter from rising materially above atmospheric pressure, forcing the withdrawn liquor into an accumulator maintained under super-atmospheric pressure, and passing acid gas from the accumulator into the liquor in the storage tank for absorbing said as.

b 4. In a system of the character described, passing cold acid liquor from a storage tank into a mixing chamber, discharging gases and vapors from a digester into the mixing chamber, and contacting the same in the latter with the acid liquor, whereby the acid liquor is pre-heated and pre-conditioned, withdrawing the pre-lieated and pre-conditioned acid liquor from the mixing chamber and thereby preventing the pressure in the latter from rising materially above atmospheric pressure, forcing the withdrawn liquor into an accumulator maintained under super-atmospheric pressure, passing acid gas from the accumulator into the liquor in the storage tank for absorbing said gas, and utilizing the pre-conditioned and re-heated acid liquor from the accumulator for precooking fibrous material in a digester.

5. In a system of the character described, continuously feeding a stream of cold acid liquor into amixing tank of suflicient capacity to provide liquid and gas spaces, relieving acid gas and vapor from a digester and contacting the same in'the mixing chamber with the cold acid liquor for pre-heating and pre-conditioning the latter, maintaining the interior of the tank at atmospheric pressure, constantly withdrawing pre-conditioned and pro-heated liquor from the mixing chamber, and forcing the withdrawn liquor into an accumulator maintained under super-atmospheric pressure.

6. In a system of the character described, pumping cold acid liquor in a substantially continuous stream into a mixing chamber of 'suflicient capacity to provide liquid and gas spaces, discharging acid gas and vapor from a digester and contacting the'same'in the mixing chamber with the cold acid liquor for pre-conditioning and pie-heating the latter, maintaining the interior of the tank at atmospheric pressure, withdrawin the preconditioned and pro-heated acid liquor from the mixing chamber, and pumping the withdrawn liquor into an accumulator.

7. In a system of the character described, pumping cold acid liquor substantially constantly from a storage chamber into a mixing chamber and spraying the same into the upper portion of the latter, discharging relief gases and vapors from a digester into the mixing chamber, and contacting the same with the sprayed acid liquor for pre-conditioning and pre-heating the latter, withdrawing the pre-conditioned and pre-heated acid liquor substantially constantly from the mixing chamber, and forcing the withdrawn liquor into an accumulator maintained under super-atmospheric pressure.

8. In a system of the character described, pumping cold acid liquor substantially constantly from a storage chamber into a mixing chamber and spraying the same into the upper portion of the latter, discharging relief gases and vapors from a digester, into the mixing chamber, and contacting the same with the sprayed acid liquor for pre-conditioning and pre-heating the latter, Withdrawing the pro-conditioned and pre-heated acid liquor substantially constantly from the mixing chamber, forcing the withdrawn liquor into an accumulator maintained under superatmospheric pressure, and passing gas from the top of the accumulator into the cold acid liquor in the storage chamber.

5). In a system of the character described, pumping cold acid liquor substantially constantly from a storage chamber into a mixing chamber and spraying the same into the upper portion of the latter,-discharging relief gases and vapors from a digester, into the mixing chamber, and contacting the same with the sprayed acid liquor for pre-conditioning and pre-heating the latter, withdrawing the pre-conditioned and pre-heated acid liquor substantially constantly from the mixing chamber, forcing the withdrawn liquor into an accumulator maintained under superatmospheric pressure, and utilizing pre-conditioned and pre-heated acid liquor from the accumulator for pre-cooking fibrous material in a digester.

10. In a system of the character described, pumping a continuous stream of cold acid liquor from a storage chamber into the up er portion'of a mixing chamber, discharging acid gas and vapor from a digester into the mixing chamber at an elevation below that "where the cold acid liquor is introduced into the same, contacting the liquor with the gases and vapors in the mixing chamber to absorb the gas and pre-condition and pre-heat the acid liquor, withdrawing pre-conditioned and pre-heated acid liquor from the mixing chamber in such manner as to prevent the pressure in the mixing chamber from rising materia'lly above atmospheric, and forcing the withdrawn liquor into an accumulator maintained at super-atmospheric pressure.

"11; In a system of the character described,

pumping a continuous stream of cold acid,

liquor from a storage chamber into the upper portion of a mixing chamber, discharging acid gas and vapor from a digester into the mixing chamber at an elevation below that where the cold acid liquor is introduced into the same, contacting the liquor with the gases and vapors in the mixing chamber to absorb the gas and pro-condition and pre-heat the acid liquor, withdrawing pre-conditioned and pre-heated acid liquor from the mixing chamber in such manner as to preveI t the pressure in the mixing chamber from rising pumping a continuous stream of cold acid liquor from a storage chamber into the upperportion of a mixing chamber, discharging acid gas and vapon from a digester into the mixing chamber at an elevation below that where the cold acid liquor is introduced into the same, contacting the liquor with the gases and vapors in the mixing chamber to absorb the gas and pre-condition and pre-heat the acid liquor, withdrawing pre-conditioned and pre-heated acid liquor from the mixing chamber in such manner as to prevent the pressure in the mixing chamber from rising materially above atmospheric, forcing the withdrawn liquor into an accumulator maintained at super-atmospheric pressure, and automatically relieving the accumulator of gas when the pressure in the accumulator reaches a predetermined maximum and passing the last mentioned gas into the cold acid liquor in the storage chamber.

13. In an apparatus of the character described, a mixing chamber, means for feedin cold acid liquor into the upper portion 0 said chamber, the mixing chamber being enlarged relativel to said means, a di ester, a relief conduit or feeding gases an vapors from the upper portion of the digester into the mixing chamber at an elevation below that where the acid liquor is fed into the mixing chamber, an accumulator, and means for withdrawing pre-conditioned and pre-heated acid liquor from the mixing chamber and for forcing the same under super-atmospheric pressure into the accumulator.

14. An apparatus as claimed in claim 13, in which the means for feeding acid liquor into the mixing chamber leads from an acid liquor stora e tank, and a valved conduit connecting t e upper portion of the accumulator with the lower portion of the acid storage tank.

15. In a process of the character described, pumping hot acid li uor into the bottom of a digester containing brous material until the digester is substantially filled with fibrous material and acid liquor, and then at the start of the cook, releasing acid liquor from the side relief of the digester.

16. In an apparatus of the character described, a mixing chamber, an acid liquor storage tank, means for feeding cold acid liquor from the storage tank into the upper portion of the mixing chamber, a digester, a relief conduit for feeding gases and vapors from the upper portion of the digester into the mixing chamber at an elevation below that where the acid liquor is fed into the mixing chamber, an accumulator, means for withdrawin preconditioned and preheated acid liquor rom the mixing chamber and for forcing the same under super-atmospheric pressure into the accumulator, a conduit connecting the upper portion of the accumulator to the lower portion of the storage tank, and a pressure operated valve in the last mentioned conduit adapted to open when the pressure in the accumulator reaches a predetermined maximum.

17. In an apparatus 'of the character described, a mixing chamber, means for feeding cold acid liquor into the upper portion of said chamber, a first digester, a relief conduit for feeding gases and vapors from the upper portion of the digester into the mixing chamber at an elevation below that where the acid liquor is fed into the mixing chamber, an accumulator, means for withdrawing preconditioned and preheated acid liquor from the mixing chamber and for feeding the same under super-atmospheric pressure into the accumulator, a second digester, and means for pumping acid 1i uor from the accumulator into the second 'gester.

18. In a system of the character described, 4

discharging high pressure relief fluids from a digester into acid liquor in apressureaccumulator, also discharging low pressure relief fluids from a digester into an enlarged mixing chamber, constantly feeding cold acid liquor into said chamber and thus utilizing the low pressure relief fluids to precondition and preheat acid liquor in the mixing chamber, withdrawing the preheated and reconditioned liquor from the mixing cham er, and forcing the withdrawn liquor into said accumulator.

19. In a system of the character described,

cumulator, and pumping preheated and preconditioned liquor from the accumulator into a digester containing fibrous material.

In testimony whereof, I have signed this specification.

THOMAS LEONIDAS DUNBAR. 

